Headspace concerns have already been mentioned, but as you are new to this I thought I would bring it up as a separate reply.
You should gauge your resized brass to check the adjustment of your resizing die before doing all 5000 too short, which will set up an excess headspace condition.
Excess headspace caused by misadjustment of the die is sometimes called "induced excess headspace" because the dimensions of your chamber haven't changed. Worn bolt lugs create a true excess headspace condition, for which the solution is usually a new barrel.
It is also possible that the cases haven't been resized enough to chamber easily, and this can be dangerous in many semi-autos as it can lead to a slamfire.
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all appeared to be in spec per my speer manual and the saami specs
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I see you are trying "dummy rounds" for chamber fit testing, and that is a good idea.
However, without a gauge, you can't measure headspace. If you are resizing brass fired in a different gun, it could already be the correct length and not need to have the shoulder pushed back a couple thousandths.
The only thing I can offer, other than getting a headspace gauge, is to try for uniformity in all parts of your process. If you have inconsistency, you will end up chasing yourself.
In theory, once you have each part of the reloading process figured out, making 1000 rounds vs. making 10 rounds is just a matter of patience.